Spark plug



7 A. H. VADNAIS Oct. 8, 1929,

SPARK rpue Filed June 11, 1923 wages reins ALEXANDER H. VADNAIS, OF OSHKOSH, WISCONSIN, A SSIGNOR TO DOUBLE VA ALARM COMPANY, INC., OF OSHKOSH, WISCONSIN, A CORPORATION OF WISCONSIN SPARK PLUG Application filed June 11,

This invention relates to spark plugs and it has among its objects the provision of an improved device of this character arranged to automatically adj ust' and maintain the sparking distance depending on the temperature conditions so as to secure prompt start-- ing and efficient operation of the engine under normal as well as abnormal temperature conditions.

The invention will be best understood from the accompanying drawings, wherein Fig. 1 is an elevation of a sparkplug embodying the invention; I

Fig. 2 is'a plan view of the lower end of 154. of the spark plug of Fig. 1;

Fig. 8 is a side elevation of the lower portion of the spark plug viewed from the right hand side of Fig. l; and r Fig. l is a vertical sectional View through the lower portion of the spark plug along the lines IVIV in Fig. 2.

With ordinary spark plugs it is often difficult to start engines because at the moment of starting the battery voltage is pulled down through the drain of heavy starting current. As a result the ignition apparatus operates at that time with reduced voltage and accordingly a reduced ignition voltage is supplied to the spark plug;

By means of my invention this difficulty in starting is overcome by providing a reduced sparking distance at. starting while,on the other hand, I retain a fixed and definite norma l sparking distance with which the spark gap operates under normal temperature conditions. To this end I provide a thermostatically responsive bridging member so arranged that when cold a part of the gap between the spark plug electrodes is' bridged over. This reduces, the sparking distance when the spark plug is cold, that is when the engine is cold, and the starting conditions are most difficult. As soon as the engine starts 7 running the full battery volta e is restored,

t the spark plug warming up in the meanwhile.

1928. Serial No. 284,284.

The increase of the temperature of the spark plug causes the thermostatically actuated" v bridging member to restore the normal gap between the spark plug electrodes and the engine runs henceforth with full sparking F electrode spacing.

A particular advantage of myarrangement is the fact that underv the normal operating conditions the sparking takes place only be tween the normal fixed electrodes, the thermostatically actuated element being out of the path of the gap at that time, thus being plete short circuit can take place between the electrodes of opposite polarity. 1 v g In the'drawlngs is shown a spark plugconstruction representing one embodiment of the inventionz Such spark plug may consist. of a metallic cylindrical shell 1 having a threaded portion 2 adapted to be screwed into the cylinder head, and the. customary head 3. Within this shell 1 is mountedan insulating bushing 4 held therein by'meansfof a gland 5 and suitable packing in the customary way.

Through the center of-the bushing 4 is sealed,-

a lead-in conductor 6 constituting the high potential terminal of the spark plug, the lower end of the conductor constituting one sparking gap electrode 7 i The other sparking electrode 8 is formed by the upwardlybent end of aconductor 9 extending from the lower end of the metal shell 1 of the plug.

The conductor 9'is grounded to the cylinder casing and constitutes the other terminal of the sparking gap. The upper end 8 of the grounded conductor 9 and the lower end 7 of the insulated conductor 6 constitutethe normal. sparkmg gap asin the plugs used. at present.

ordinary spark .stituting an enlarged tip adjacent the gap between the main sparking electrodes 7 and 8. According to the invention one of the two fixed sparking electrodes, in this case the grounded electrode 8, is somewhat offset against the other electrode The thermostatic bar 11 is so arranged that under low temperature conditions its free end tip 13v abuts and rests against the offset portion of the grounded gap electrode 8, a part of the tip extending close to the insulated high potential electrode 7 on the gap. In this way a reduced spark gap is provided between the upper end of the tip 13 and the side of the high voltage sparking electrode 7. WVhen the engine is cold the spark will pass through this reduced gap which is shown best at 15 in Fig. 4. If the temperature rises, the bar 11 turns outwardly restoring the full gap width between the sparking electrodes 7 and 8. p p

The foregoing arrangement prevents. positively short circuiting of the spark gap no matter how low the temperature of the engine is because'the minimum spark gap distance is determined by the offset relationship ofthe two main spark gap electrodes 7, 8. A similar result could be obtained without oflsetting the main electrodes by providing a special projecting abutment or stop either on "the grounded electrode 8 or on the tip 13 or on both, or by some other arrangement that will suggest itself to those skilled in the art.

My arrangement also secures a definite sparking gap under normal operating condi tions becau'seof the'fixed positioning of the two main gap electrodes '2' and 8, and thus prevents any disturbance because of excessive gap length when the engine warmsup to high operation of the engine and the danger of bridging the spark gap are thus eliminated while retaining all the advantages of a thermostatically adjustable, varying spark gap.

' In the arrangement shown hereinabove the thermostatic bar and the auxiliary bridging electrode 13 are directly grounded and conductively connected to the metallic shell 1 of the spark gap, this arrangement being advantageous because it avoids double sparking when the electrode tip 18 moves outwardly under rising temperature conditions. However, in some cases such double sparking ac-- tion may be desired in which case the thermostatic bar 11 may be insulatingly supported on the lower end of the spark plug.

The invention is not limited to the particular details of construction shown hereinabove and many modifications thereof will suggest themselves to those skilled in the art.

It is accordingly desired that the appended claims be given a broad construction commensurate with the scope of the invention within the art.

I claim 1 1. In a spark plug, a pair of fixed gap electrodes and thermostatically controlled means for partially bridging'the gap between the electrodes. v

2. In a spark plug, a pair of fixed gap electrodes and thermostatically controlled means for partially bridging the gap between the electrodes, said means being so arranged as to permit variation of the gap length between a fixed minimum and fixed maximum value.

3. In a spark plug, a pair of gap electrodes, a thermostatic element, and a bridging electrode actuated by said thermostatic element to partially shorten said gap. I

I 4. In a spark plug, a pair of gap electrodes and thermostatically actuated means for varying the gap length between a fixed minimum and fixed maximum value.

5. In a spark plug, a pair of gap electrodes and a bimetallic element for varying the gap length between a fixed minimum and a fixed maximum value.

6. In a spark plug, an insulated gap electrode, a grounded gap electrode, and means associated with said grounded gap electrode for varying the active gap length between a fixed minimum and a fixed maximum value.

7 In a spark plug, an insulated gap electrode, a grounded gap electrode, a bridging electrode, and thermostatically actuated means for moving said bridging electrode to vary the gap lengths between said grounded electrode and said insulatedelectrode, said grounded electrode acting as a stop for limiting the movement of said bridging electrode to secure a minimum spark gap length.

8. In a spark plug, a pair of fixed electrodes, a bridging electrode, and thermostatically actuated means to move said bridging electrode to reduce the spark gap length between said electrodes, one of said fixed electrodes being arranged to stop the movement of said bridging electrode to. secure a minimum spark gap length.

9. In a spark plug, a fixed insulatin electrode, a fixed grounded gap electrode, abridgios ing electrode, and thermostatically actuated means for moving said bridging electrode to reduce the gap length between said fixed elec-' trodes, said grounded fixed electrode being arranged to limit the movement of said bridging electrode so as to produce a minimum spark gap.

In testimony whereof I have hereunto subscribed my name this 7 th day of June, 1928. ALEXANDER H. VADNAIS. 

